1. Field of the Invention
This invention relates generally to a method and apparatus for removing dissolved or emulsified salts from crude tall oil derived from sulfate soaps, and more particularly to a method and apparatus in which crude tall oil and water at predetermined temperature, pressure and flow rate values undergo mass transfer.
2. Description of the Prior Art
Crude tall oil derived from the conventional discontinuous or continuous breakdown of sulfate soaps of cellulose extraction retains a residual amount of dissolved or emulsified alkali sulfates. The amount of dissolved or emulsified salts remaining in the crude tall oil, which varies within relatively broad limits depending on the breakdown method used, can be derived from the ash content after incineration of the tall oil. Approximately 0.1-0.2% by weight of ash accumulation, which corresponds to 0.23-0.46% by weight of sodium sulfate is common. Since these salts do not evaporate under the distillation conditions of tall oil distillation for the separation of pitch, they remain in the non-evaporated part during all evaporation and distillation steps during the preparation of tall oil.
The above-noted conditions limits the total distillate portion obtainable. A loss of only a few weight percents makes a considerable economic difference. Moreover, such salts induce a rather strong incrustation upon evaporator heating surfaces by forming salt deposits thereon even with careful evaporation, resulting in a highly undesirable drop in output. A careful cleaning at relatively short intervals of time is therefore required to eliminate these incrustations. Such cleaning considering the thermal and especially the oxidiative sensitivity is very time-consuming and thus very expensive, because such cleaning time further diminishes output, which has been noticeably lowered already by the diminished passage of heat resulting from the above-noted incrustation.
It is known in the continuous breakdown of sulfate soap by sulfuric acid that a subsequent hot water wash of the crude tall oil accumulating during the decomposition of the soap can be performed at 70.degree.-80.degree. C.; however, in the subsequent distillative work-up the aforementioned problems can not be eliminated.